Method of electroplating a plurality of conductive fingers

ABSTRACT

A method of electroplating may include placing a pair of conductive fingers in proximity to an edge of a circuit board, where the pair are coupled to be electrically isolated, and where the pair are substantially longitudinally oriented away from the edge. A trace electrically couples the pair of conductive fingers via a shortest path between the pair of conductive fingers. A plating bar is electrically coupled to one of the pair of conductive fingers and thereafter electroplating the pair of conductive fingers via the plating bar. Subsequent to electroplating, laser drilling the trace to electrically isolate the pair of conductive fingers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/364,728filed on Feb. 27, 2006. The disclosure of the above application isincorporated herein by reference.

BACKGROUND

The conventional process for electroplating conductive fingers ofelectrical connectors on circuit boards is to extend the fingers beyondthe edge of the board and then add a plating bar to electrically connectthe fingers. This does not work well when the board design requiresshortened fingers that do not extend to the edge of the board. Thecurrent method leaves stubs and traces in valuable areas of real estateon the board, and is difficult to implement.

There is a need, not met in the prior art, of a method forelectroplating a plurality of conductive fingers that is simple,cost-effective and does not leave stubs and traces on useable circuitboard real estate. Accordingly, there is a significant need for a methodthat overcomes the deficiencies of the prior art outlined above.

DRAWINGS

Representative elements, operational features, applications and/oradvantages of the present invention reside inter alia in the details ofconstruction and operation as more fully hereafter depicted, describedand claimed—reference being made to the accompanying drawings forming apart hereof, wherein like numerals refer to like parts throughout. Otherelements, operational features, applications and/or advantages willbecome apparent in light of certain exemplary embodiments recited in theDetailed Description, wherein:

FIG. 1 representatively illustrates a prior art method of electroplatingconductive fingers on a circuit board;

FIG. 2 representatively illustrates another prior art method ofelectroplating conductive fingers on a circuit board;

FIG. 3 representatively illustrates a method of electroplatingconductive fingers in accordance with an exemplary embodiment of thepresent invention; and

FIG. 4 further representatively illustrates a method of electroplatingconductive fingers in accordance with an exemplary embodiment of thepresent invention.

Elements in the Figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale. For example, the dimensions ofsome of the elements in the Figures may be exaggerated relative to otherelements to help improve understanding of various embodiments of thepresent invention. Furthermore, the terms “first”, “second”, and thelike herein, if any, are used inter alia for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. Moreover, the terms “front”, “back”, “top”,“bottom”, “over”, “under”, and the like in the Description and/or in theClaims, if any, are generally employed for descriptive purposes and notnecessarily for comprehensively describing exclusive relative position.Any of the preceding terms so used may be interchanged under appropriatecircumstances such that various embodiments of the invention describedherein may be capable of operation in other configurations and/ororientations than those explicitly illustrated or otherwise described.

DETAILED DESCRIPTION

The following representative descriptions of the present inventiongenerally relate to exemplary embodiments and the inventor's conceptionof the best mode, and are not intended to limit the applicability orconfiguration of the invention in any way. Rather, the followingdescription is intended to provide convenient illustrations forimplementing various embodiments of the invention. As will becomeapparent, changes may be made in the function and/or arrangement of anyof the elements described in the disclosed exemplary embodiments withoutdeparting from the spirit and scope of the invention. The presentinvention is not limited to implementation by any particular set ofelements, and the description herein is merely representational of oneembodiment.

The terms “a” or “an”, as used herein, are defined as one, or more thanone. The term “plurality,” as used herein, is defined as two, or morethan two. The term “another,” as used herein, is defined as at least asecond or more. The terms “including” and/or “having,” as used herein,are defined as comprising (i.e., open language). The term “coupled,” asused herein, is defined as connected, although not necessarily directly,and not necessarily mechanically.

FIG. 1 representatively illustrates a prior art method of electroplatingconductive fingers 104 on a circuit board 100. The circuit board 100depicted in FIG. 1 may be an edge connector for mounting the circuitboard and electrically connecting conductive fingers 104 to contactelements in a connecting member into which the edge connector may beinserted. More particularly, an edge connector may include contactelements positioned on its surface 101 coupled to engage similarelements or pins in a housing when the edge connected is insertedtherein. Upon inserting the edge connector into a slot of connectingmember, the fingers electrically engage the contact elements in theconnecting member to complete the electrical path from the conductivefingers 104 on the circuit board 100 to the conductive traces in theslot of the connecting member.

Most circuit boards are composed of between one and sixteen conductivelayers separated and supported by layers of insulating material(substrates) laminated (glued) together. Layers may be connectedtogether through drilled holes called vias. Either the holes areelectroplated or small rivets are inserted to electrically connect theconductive layers. High-density circuit boards may have blind vias,which are visible only on one surface, or buried vias, which are visibleon neither.

Low-end consumer grade circuit board substrates frequently are made ofpaper impregnated with phenolic resin. High-end consumer and industrialcircuit board substrates are typically made of a material designatedFR-4. This consists of a woven fiberglass mat impregnated with a flameresistant epoxy resin.

The vast majority of circuit boards are made by adhering a layer ofcopper over the entire substrate, sometimes on both sides, (creating ablank circuit board) then removing unwanted copper after applying atemporary mask (e.g. by etching in an acid), leaving only the desiredcopper traces. A few circuit boards are made by adding traces to thebare substrate.

Plurality of conductive fingers 104 must be able to withstand repeatedinsertion and removal of the circuit board into the connecting member.The frictional wear is required to be kept at a minimum. Therefore, theconductive fingers 104, which are often copper, are electroplated with amore robust conductive material such as gold, nickel or some combinationthereof.

In a non-limiting example of electroplating, gold plating is often usedin electronics to provide a corrosion-resistant electrically conductivelayer on copper, typically in electrical connectors and printed circuitboards. With direct gold-on-copper plating, the copper atoms have thetendency to diffuse through the gold layer, causing tarnishing of itssurface and formation of an oxide/sulfide layer. A layer of a suitablebarrier metal, usually nickel, may therefore be deposited on the coppersubstrate, forming a copper-nickel-gold sandwich. Both the nickel andgold layers are usually deposited by electroplating.

As is known in the art, electroplating is the coating of an electricallyconductive item with a layer of metal using electrical current. Theresult is a thin, smooth, even coat of metal on the object. The processused in electroplating is called electro-deposition. The item to becoated (circuit board 100) is placed into a container containing asolution of one or more metal salts. The circuit board 100 is connectedto an electrical circuit via the plating bar 106, forming the cathode(negative) of the circuit while an electrode typically of the same metalto be plated forms the anode (positive). When an electrical current ispassed through the circuit, metal ions in the solution are attracted tothe conductive fingers 104. The result is a layer of metal on theconductive fingers 104. The anode and cathode in the electroplating cellare connected to an external supply of direct current, a battery, ormore commonly a rectifier. The anode is connected to the positiveterminal of the supply, and the cathode (article to be “plated”) isconnected to the negative terminal, usually via a plating bar 106. Whenan external power supply is switched on, the metal at the anode isoxidized from the 0 valence state to form cations with a positivecharge. These cations associate with the anions in the solution. Thecations are reduced at the cathode to deposit in the metallic, 0 valencestate.

The conductive fingers 104 shown in FIG. 1 run to the edge 102 of thecircuit board 100. This makes the addition of the plating bar 106 forelectroplating easy as the conductive fingers 104 are at the edge of thecircuit board 100. So when the plating bar 106 is removed afterelectroplating (often with a portion of the circuit board 100), thereare no stubs left and a clean cut is possible.

FIG. 2 representatively illustrates another prior art method ofelectroplating conductive fingers 204 on the surface 201 of a circuitboard 200. In the circuit board 200 depicted in FIG. 2, a pair ofconductive fingers 209 are present with neither at the edge 202 of thecircuit board 200. Both the front conductive finger 210 and the rearconductive finger 212 are set back from edge 202. As shown, frontconductive finger 210 and rear conductive finger 212 are longitudinallyoriented away from edge 202. Pair of conductive fingers 209 may be insubstantially in line with each other as shown or substantially offsetfrom each other.

In the prior art, in order to electroplate pair of conductive fingers209, both front conductive finger 210 and rear conductive finger 212must be connected to plating bar 206. Front conductive finger 210 mayinclude stubs to edge 202 to connect with plating bar 206 without thestubs taking up useable circuit board real estate. However, each rearconductive finger 212 includes trace 215 to electrically couple itselfto a common point 216, which is then electrically coupled to plating bar206 via a conductive trace. In the alternative, one or more of the rearconductive fingers 212 may be directly connected to plating bar 206using its own dedicated trace 215. Subsequent to electroplating, a viamay be drilled out at common point 216 to electrically isolate each rearconductive finger 212 from plating bar 206.

In the prior art described above, after common point 216 is drilled out,the traces 215 remain on useable circuit board real estate. The traces215 may be removed, which is a lengthy, manual and expensive process, orthey may be left behind, thereby rendering useless that circuit boardreal estate. Both of these alternatives have the disadvantage ofincreased expense and reduced efficiency.

FIG. 3 representatively illustrates a method of electroplatingconductive fingers 304 in accordance with an exemplary embodiment of thepresent invention. The embodiment shown in FIG. 3 includes a circuitboard 300 having an edge 302 and a surface 301. On the surface 301 are aplurality of conductive fingers 304.

Plurality of conductive fingers 304 may include any number of pairs ofconductive fingers 309 comprising a front conductive finger 310 and arear conductive finger 312. Pair of conductive fingers 309 are presentwith neither at the edge 302 of the circuit board 300. Both the frontconductive finger 310 and the rear conductive finger 312 are set backfrom edge 302. In an embodiment, front conductive finger 310 may beinset a first distance 311 from edge 302, while rear conductive finger312 may be inset a second distance 313 from front edge, where seconddistance 313 is greater than first distance 311.

As shown, front conductive finger 310 and rear conductive finger 312 arelongitudinally oriented away from edge 302. Pair of conductive fingers309 may be in substantially in line with each other as shown orsubstantially offset from each other.

Circuit board 300 may also include a plating bar portion 317 that isremovable subsequent to electroplating plurality of fingers 304. Platingbar portion 317 includes plating bar 306, which may be used for anelectrical connection in the electroplating process described above.

In an embodiment, once plating bar portion 317 is removed, circuit board300 may be an Advanced Mezzanine Card (AMC) module suitable for use in aMicroTCA chassis, complying with the MicroTCA standard as defined inPICMG.®. MicroTCA.0 Draft 0.6—Micro Telecom Compute Architecture BaseSpecification (and subsequent revisions). The embodiment of theinvention is not limited to the use of these standards, and the use ofother standards is within the scope of the invention.

MicroTCA is a collection of interconnected elements including at leastone Advanced Mezzanine Card module, at least one virtual carrier manager(VCM) and the interconnect, power, cooling and mechanical resourcesneeded to support them. A typical prior art MicroTCA system may consistof twelve AMC modules, one (and optionally two for redundancy) virtualcarrier managers coupled to a backplane 103. AMC modules are specifiedin the Advanced Mezzanine Card Base Specification (PICMG.®. AMC.0 RC1.1and subsequent revisions). VCM's are specified in the MicroTCAspecification—MicroTCA.0 Draft 0.6—Micro Telecom Compute ArchitectureBase Specification (and subsequent revisions).

AMC modules can be single-width, double-width, full-height, half-heightmodules or any combination thereof as defined by the AMC specification.A VCM acts as a virtual carrier card which emulates the requirements ofthe carrier card defined in the Advanced Mezzanine Card BaseSpecification (PICMG.®. AMC.0 RC1.1) to properly host AMC modules.Carrier card functional requirements include power delivery,interconnects, Intelligent Platform Management Interface (IPMI)management, and the like. VCM combines the control and managementinfrastructure, interconnect fabric resources and the power controlinfrastructure for the AMC modules into a single unit. A VCM comprisesthese common elements that are shared by all AMC modules, on one or moreAMC modules, or a combination thereof.

The circuit board 300 is not limited to being an AMC module and can beany circuit board having two or more conductive fingers inset a distancefrom an edge of the circuit board.

As shown in FIG. 3, a trace 315 electrically couples front conductivefinger 310 and rear conductive ginger 312 via a shortest path 322between front conductive finger 310 and conductive finger 312. Trace 315may be placed at the same time, prior to, or after the pair ofconductive fingers 309 are placed on circuit board 300. Trace 315 may beany conductive material such that front conductive finger 310 and rearconductive finger 312 are electrically coupled.

Front conductive fingers 310 may be electrically coupled to plating bar306 via additional traces as shown. Once traces 315 are in place,plating bar may be electrically coupled to plurality of fingers 304without the additional traces over the circuit board as shown in theprior art. This has the advantage of not wasting valuable and useablecircuit board real estate and not having to remove the additional tracelines shown in FIG. 2.

Circuit board 300 may then have plurality of conductive fingers 304electroplated by attaching plating bar 306 to an electrical source asdescribed above. Plurality of conductive fingers 304 may beelectroplated with a conductive material to suite a particularapplication. For example and without limitation, plurality of conductivefingers 304 may be electroplated with gold, nickel or a combination ofgold and nickel to provide plurality of conductive fingers 304resistance to wear.

Subsequent to electroplating, trace 315 may be removed by laser drilling320 using, for example and without limitation, a laser via drill such asa high-density interconnect (HDI) laser drill, a non-plated laser drill(NPLD), and the like. Unlike conventional HDI laser drilling, in thepresent embodiment the via created with the laser drilling of the traceis not plated, so the pair of conductive fingers 304 are electricallyisolated from each other. Effectively, the laser drilling destroys, inpart or in whole, the trace 315 and severs the trace 315 so that thepair of conductive fingers 304 is electrically isolated. Since trace 315was placed on the shortest path 322 between the pair of conductivefingers 304, trace 315 is easily severed using laser drilling. Thisleaves two longitudinally oriented conductive fingers 323 that areelectroplated and electrically isolated from each other, without leavingbehind unwanted electrical traces or having to remove unwantedelectrical traces.

Also subsequent to electroplating, plating bar 306 and plating barportion 317 may be severed from circuit board 300. This now permits theuse of circuit board 300 in uses, for example, as an AMC moduledescribed above.

FIG. 4 further representatively illustrates a method of electroplatingconductive fingers in accordance with an exemplary embodiment of thepresent invention. As shown in FIG. 4, a circuit board 400 having anedge 402 and surface 401 with a front conductive finger 410 and a rearconductive finger 412 on the surface 401. In an embodiment, each offront conductive finger 410 and the rear conductive finger 412 arecomprised of a first conductive material 430, and are electroplated witha second conductive material 432. The first conductive material 430 maybe copper, and the like. The second conductive material may be nickel,gold, a combination of nickel and gold, and the like. The invention isnot limited to one electroplated material (second conductive material432). Any number of conductive materials and any number of layers may beelectroplated and be within the scope of the invention.

In an embodiment, laser drill 420 may be used to sever and/or destroytrace 315 by drilling substantially down to a capture pad 440 in circuitboard 400. In the prior art, the via created by laser drilling is platedwith a conductive material to electrically couple first conductivefinger 410 and second conductive finger 412 to each other and/or tocapture pad 440. In the present embodiment, the via created by laserdrilling is not electroplated and first conductive finger 410 and secondconductive finger 412 are not electrically coupled to each other orcapture pad 440.

In embodiment, edge 402 of the circuit board 400 is coupled toelectrically interface with a connecting member 450 such as a slot,motherboard, and the like. In an embodiment, circuit board 400 is anedge connector coupled to be inserted into the connecting member 450.First conductive finger 410 and second conductive finger 412 are coupledto interface with electrical pads 452 in connecting member.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments. However, it will beappreciated that various modifications and changes may be made withoutdeparting from the scope of the present invention as set forth in theclaims below. The specification and figures are to be regarded in anillustrative manner, rather than a restrictive one and all suchmodifications are intended to be included within the scope of thepresent invention. Accordingly, the scope of the invention should bedetermined by the claims appended hereto and their legal equivalentsrather than by merely the examples described above.

For example, the steps recited in any method or process claims may beexecuted in any order and are not limited to the specific orderpresented in the claims. Additionally, the components and/or elementsrecited in any apparatus claims may be assembled or otherwiseoperationally configured in a variety of permutations to producesubstantially the same result as the present invention and areaccordingly not limited to the specific configuration recited in theclaims.

Benefits, other advantages and solutions to problems have been describedabove with regard to particular embodiments; however, any benefit,advantage, solution to problem or any element that may cause anyparticular benefit, advantage or solution to occur or to become morepronounced are not to be construed as critical, required or essentialfeatures or components of any or all the claims.

Other combinations and/or modifications of the above-describedstructures, arrangements, applications, proportions, elements, materialsor components used in the practice of the present invention, in additionto those not specifically recited, may be varied or otherwiseparticularly adapted to specific environments, manufacturingspecifications, design parameters or other operating requirementswithout departing from the general principles of the same.

1. A circuit board comprising: a front conductive finger placed on asurface of the circuit board inset a first distance from an edge; a rearconductive finger placed on the surface and inset a second distance fromthe edge, where the second distance is larger than the first distance; atrace electrically coupling the front conductive finger to the rearconductive finger via a shortest path between the front conductivefinger and the rear conductive finger; a plating bar coupled to thefront conductive finger, wherein the front conductive finger and therear conductive finger are electroplated via the plating bar and whereinthe trace is laser driller to electrically isolate the front conductivefinger from the rear conductive finger.